Scabies Scabies is an itchy rash caused by the parasitic mite Sarcptes scabiei. Scabies has caused pruritic infestatin in humans fr ver 2,500 years. The female scabies mite is abut 0.4 mm lng, and the male is 0.2mm. After mating n the skin surface, the male dies and the female mite tunnels int the epidermis, and depsits eggs alng the burrw. Develpment frm egg t adult takes abut 10-15 days. Adult mites then return t the skin surface t multiply. Mites die after 4-6 weeks. An average hst harburs 10-12 mites. This may be greatly increased in immuncmprmised patients). Cntact Classical scabies requires skin cntact f 10-15 minutes fr mites t be passed frm ne hst t anther. Crusted scabies (a mre severe variety, see belw) can als be transmitted via bedding, twels, clthes and furniture. Female mites can mve at up t 2.5 cm per minute but they d nt jump r fly. Epidemilgy Scabies is a cmmn public health prblem with an estimated 300 millin cases prevalent wrldwide. It is ften difficult t diagnse due t the spectrum f assciated signs and symptms and its clinical mimicry f ther cnditins. Risk factrs Overcrwding. Pverty, pr nutritinal status. Hmelessness. Pr hygiene. Institutins. Residential care hmes in the UK, refugee camps in sme parts f the wrld. Dementia. Sexual cntact. Children, especially in develping cuntries. Immune suppressin (eg, HIV infectin). Presentatin Signs and symptms develp after 3-4 weeks hwever the infectin can be transmitted t thers during this asymptmatic phase.
Infected cntacts may be asymptmatic fr up t a mnth which is why treatment f all significant cntacts is needed. Symptms reappear within 1-3 days if the persn is reinfested due t prir sensitisatin. The mst cmmn presenting symptm is widespread itching. This develps as an allergic reactin t infectin, usually 4-6 weeks after infestatin. This is usually wrse at night and when the persn is warm. A histry f several family members all suffering with itch is strngly suggestive f scabies. Scratching predispses t secndary bacterial infectin. On examinatin the skin changes vary. Lesins may be papules, vesicles, pustules, and ndules. Erythematus papular r vesicular lesins are usually seen in the sites f the burrws. The mre widespread, symmetrical, itchy, papular eruptin is nt in the areas f burrws r bvius mite activity. This is mst cmmnly seen arund the axillae, the periarelar regin f the breasts in wmen, and the abdmen, buttcks, and thighs. Excriatin marks are cmmn and may be mre marked than the underlying rash. Scabies f the leg Burrws may be visible as fine, wavy, greyish, dark r silvery lines, 2-15 mm lng, smetimes with a minute speck (the mite) at the clsed end. They are mst ften seen in the web spaces between fingers, inside f the wrists and elbws, axilla, ankles, feet, buttck areas, male genitalia and peri-arelar area in wmen.
Scabies - burrws n a finger Ndules may develp. These ccur particularly at the elbws, anterir axillary flds, penis, and scrtum. They are firm, dull red r brwn, and may be very itchy. They may persist fr weeks r mnths after treatment and d nt necessarily indicate active infestatin, but rather the result f a chrnic allergic reactin t the mite. Inflammatry papules and ndules n the male genitalia, smetimes with visible burrws, are diagnstic f scabies. Thick skin is relatively resistant, s sparing is nrmally seen f the sles f the feet and upper back regin in adults. Even a single burrw is pathgnmnic but burrws are ften bliterated by bathing, scratching, crusts, r superinfectin. Papules and vesicles frequently develp int excriatins, eczema exacerbatins, secndary infectins and crusts. Differential diagnsis Misdiagnsis is cmmn and ther skin disrders, particularly thse causing itching, shuld be cnsidered. Investigatins The diagnsis is largely clinical. A magnifying lens may help in identificatin f burrws r even ccasinally mites. Management All members f the husehld, clse cntacts, and sexual cntacts shuld be treated simultaneusly with the index patient. It is imprtant that all cntacts apply treatment n the same day t reduce the risk f re-infestatin frm an untreated cntact. Patients shuld be advised t avid clse bdy cntact until they and their partner(s) have cmpleted the treatment. The primary methd f treatment fr scabies is by tpical applicatin f a parasiticidal preparatin vernight t the whle bdy frm head t te. Apply treatment t the whle bdy, including the scalp, neck, face, and ears, and especially between the fingers and
tes and under the nails. Treatment shuld nt be applied after a ht bath (as this increases systemic absrptin and remves the drug frm its treatment site). If the hands are washed, the liquid r cream must be reapplied. First-line: permethrin 5% dermal cream Secnd-line: malathin 0.5% aqueus liquid. Oral ivermectin (as a single ral dse f 200 micrgrams/kg) is available n a named-patient basis as an adjunct t tpical treatment fr crusted ('Nrwegian') scabies. This treatment is usually initiated n specialist advice. This shuld be repeated a week later. Clthes, twels, and bed linen shuld be machine-washed (at 50 C r abve) t prevent re-infestatin and transmissin. Items that cannt be washed can be kept in plastic bags fr at least 72 hurs t cntain the mites until they die. The risk f transmissin f scabies is lw in schls and children can return t schl after the first applicatin f treatment has been cmpleted. Itch Antihistamines are f little help in treating pruritus. A sedative ral antihistamine at night may help with sleeping and s reduce scratching. Crtamitn cream r ltin has sthing qualities and may help t relieve the itch caused by scabies. Lw-dse sterid creams r simple emllients and misturisers stred in the fridge may als ease discmfrt. Itching can persist fr up t 3 weeks after treatment. Warn the patient this des nt mean the treatment has failed. Treatment failure Shuld be cnsidered where: Itching persists mre than 6 weeks after the first applicatin f an insecticide. Treatment was nt applied as instructed r nt c-rdinated between clse cntacts. New burrws appear. If incrrectly applied treatment has failed, repeat, ensuring everyne clearly understands the instructins. Where crrectly applied treatment has nt wrked, give a curse f a different parasiticidal preparatin. This reduces the develpment f resistance t the medicatin. Secndary bacterial infectins shuld be treated with antibitics if significant. Offered full STI screening
Nte: Seek specialist advice fr children under 2 mnths ld - scabies is rare in this age grup. Breast-feeding r pregnant wmen with scabies can be treated with permethrin 5% dermal cream (r malathin if permethrin is cntra-indicated), althugh neither is specifically licensed fr such; there is, hwever, n indicatin that either prduct is harmful t the fetus r child. Breast-feeding mthers shuld remve the liquid r cream frm the nipples befre breast-feeding, and reapply treatment afterwards. Cmplicatins Scabies can cause flaring r reactivatin f eczema r psriasis. Secndary bacterial infectin. This is a cause f much mrbidity and mrtality, especially in the develping wrld. Particularly invlved are Staphylcccus aureus r Streptcccus pygenes. Cellulitis, impetig and abscesses may be the result, and bacterial skin infectin can further predispse t invasive infectin and sepsis. S. pygenes infectin secndary t scabies is a risk factr fr acute pst-streptcccal glmerulnephritis and pssibly acute rheumatic fever. Crusted scabies has a high mrtality rate due t secndary sepsis in the immunsuppressed. Prgnsis Scabies persists indefinitely unless treated. Treatment, if applied crrectly, has a high chance f cure. In endemic areas, re-infestatin is likely. Crusted ('Nrwegian') scabies Crusted scabies is a hyper-infestatin with thusands f mites present in exfliating scales, due t the hst's insufficient immune respnse. Thse at risk include: The immunsuppressed (eg, HIV infectin, leukaemia r lymphma). Elderly patients. Thse with decreased peripheral sensatin. Hyperkerattic crusted lesins typically affect the hands, feet, nails, scalp and ears, but all areas f skin, including the scalp and trunk, may be invlved. Crusted scabies is a hyperkerattic skin disease resembling psriasis. It may present with generalised lymphadenpathy. It ften becmes secndarily infected. This frm f scabies is very cntagius and is far mre difficult t eradicate than classical scabies.